Evaluation of the reconstruction of seed positions from stereo and orthogonal radiographs for routine radiotherapy planning.
Brachytherapy, which refers to short-distance treatment via implanted sources, requires an accurate knowledge of the dose distribution in the implant volume. A critical step in the determination of the dose distribution involves an accurate reconstruction of seed positions. Stereo and orthogonal radiographs offer two distinct imaging techniques for determining the seed positions in the implant volume. This work is an attempt to study the effects of random errors associated with the three-dimensional reconstruction of a two-plane seed implant from stereo and orthogonal radiographs. The uncertainty in coordinates is expressed as the standard deviation of the measurements. To assess the geometric accuracy of the stereo and orthogonal methods, the computer-reconstructed coordinates of each seed are compared with the measured and manually calculated coordinates. The uncertainties in the coordinates and relative positions of seeds are also estimated by considering the propagation of errors in the reconstructed parameters. The isodose contours surrounding the implant are obtained for both methods. Using a sonic digitizer to input the data, it was found that seed coordinates and relative seed positions can be obtained satisfactorily from stereo radiographs. The uncertainties were compared with the values reported in the literature. Suggestions are made to reduce the uncertainties in the reconstruction of coordinates with the stereo method.
Niroomand-Rad
A
A
Department of Radiation Medicine, Georgetown University Medical Center, Washington, D.C. 20007.
Thomadsen
B R
BR
D001918:Brachytherapy; D006801:Humans; D007091:Image Processing, Computer-Assisted; D011880:Radiotherapy Planning, Computer-Assisted